A telescopic gun sight or a riflescope is a device used to provide an accurate point of aim for firearms such as rifles, handguns and shotguns. It is used with other types of weapons such as bows and crossbows as well. A telescopic sight can dramatically improve the functionality of a firearm by providing the shooter with a simple yet highly accurate means for aiming at distant targets.
In telescopic sights, the “point of aim” is usually designated by a reticle or cross hairs. Telescopic sights are also equipped with two control knobs for elevation (up-down) and windage (left-right) adjustments. These knobs allow for precise vertical and horizontal movement of the reticle so that the sight's point of aim can be aligned with the firearm's “point of impact”.
For descriptions of the conventional mechanical methods commonly used to adjust the reticle within a telescopic sight see, for example, U.S. Pat. No. 2,955,512 issued Oct. 11, 1960 to Kollmorgen et al., U.S. Pat. No. 3,161,716 issued Dec. 16, 1964 to Burris et al., U.S. Pat. No. 5,463,495 issued Oct. 31, 1995 to Murg, and U.S. Pat. No. 5,615,487 issued Apr. 1, 1997 to Tomita.
An optical method for adjusting the point of aim in telescopic gun sights has been disclosed in U.S. Pat. No. 8,749,887 issued Jun. 10, 2014 to the present applicant. This patent teaches the use of two wedge prisms which move linearly along the optical axis for shifting the image formed by the objective on the reticle. This novel optical method overcomes many of the drawbacks associated with the conventional mechanical methods.
The present application teaches an alternative optical method for adjusting the point of aim in telescopic gun sights. Here, counter-rotating wedge prisms mounted in a fixed location on the optical axis are used. This method leads to a more compact solution. Certain optical abberations associated with the linear movement method are also eliminated.
Beam steering using a pair of rotatable wedge prisms is well-known in optical engineering. Such prisms are commonly referred to as Risley prisms after their inventor Dr. Samuel D. Risley (1845-1920). Examples of using Risley prisms for laser beam scanning or steering the field of view of various optical instruments can be found in U.S. Pat. No. 4,118,109 issued Oct. 3, 1978 to Crawford et al., U.S. Pat. No. 3,378,687 issued Apr. 16, 1968 to Schepler, U.S. Pat. No. 4,405,203 issued Sep. 20, 1983 to Wallner, U.S. Pat. No. 6,061,945 issued May 16, 2000 to Wallace et al., U.S. Pat. No. 8,294,080 issued Oct. 23, 2012 to Rana, U.S. Pat. No. 8,363,321 issued Jun. 29, 2013 to Pochapsky, and U.S. Pat. No. 8,400,700 issued Mar. 19, 2013 to Adams et al.
A direct-vision (i.e. non-telescopic) bow sight which uses Risley prisms for adjusting the point of aim has been disclosed in U.S. Pat. No. 2,534,946 issued Dec. 19, 1950 to Bradley. A non-magnifying reflex sight that uses Risley prisms to adjust the point of aim is disclosed in U.S. Pat. No. 2,458,831 issued Jan. 11, 1949 to Cady.
An abandoned patent application by Strong (Appl. Ser. No. 10/638,119 filed on Aug. 8, 2003) discloses a telescopic gun sight that uses rotating prisms for adjusting the sight's point of aim Strong teaches mounting the prisms in front of the objective lens as shown in FIGS. 1 and 2 of his disclosure.
The present invention is distinct from the above mentioned prior art because the rotating prisms are used inside a telescopic sight and are positioned after the objective lens. Implications and advantages of positioning the rotating prims after the objective lens are discussed in detail in subsequent sections.